Déborah P. Rondanini

Physiological responses of spring rapeseed (Brassica napus) to red/far‐red ratios and irradiance during pre‐ and post‐flowering stages

Early shade signals promote the shade avoidance syndrome (SAS) which causes, among others, petiole and shoot elongation and upward leaf position. In spite of its relevance, these photomorphogenic responses have not been deeply studied in rapeseed (Brassica napus). In contrast to other crops like maize and wheat, rapeseed has a complex developmental phenotypic pattern as it evolves from an initial rosette to the main stem elongation and an indeterminate growth of floral raceme. In this work, we analyzed (1) morphological and physiological responses at individual level due to low red/far-red (R/FR) ratio during plant development, and (2) changes in biomass allocation, grain yield and composition at crop level in response to high R/FR ratio and low irradiance in two modern spring rapeseed genotypes. We carried out pot and field experiments modifying R/FR ratios and irradiance at vegetative or reproductive stages. In pot experiments, low R/FR ratio increased the petiole and lamina length, upward leaf position and also accelerated leaf senescence. Furthermore, low R/FR ratio reduced main floral raceme and increased floral branching with higher remobilization of soluble carbohydrates from the stems. In field experiments, low irradiance during post-flowering reduced grain yield, harvest index and grain oil content, and high R/FR ratio reaching the crop partially alleviated such effects. We conclude that photomorphogenic signals are integrated early during the vegetative growth, and irradiance has stronger effects than R/FR signals at rapeseed crop level.

Nitrogen × sulfur interaction on fertiliser-use efficiency in bread wheat genotypes from the Argentine Pampas

Abstract. Wheat crop response to sulfur (S) depends on nitrogen (N) level, genotype and environmental conditions, demonstrating strong genotype × environment × nutrients interactions. The agronomic-use efficiency of both nutrients has not been evaluated in a wide range of modern genotypes differing in their cycle length and baking quality. The aim of this study was to analyse the effect of N and S fertilisation on yield components and use efficiency of both nutrients in 24 modern, high-yielding bread wheat genotypes (including long and short crop cycles) grown in contrasting environments in the Humid Pampa of Argentina. Two experiments were conducted under contrasting seasonal conditions on a Mollisol in Azul, Buenos Aires. Significant effects of N (range 15–200 kg N ha–1) on grain yield were observed in all genotypes. By contrast, responses to S (30–100 kg S ha–1) were found only at high N level in low soil-fertility environments, differing between long and short cycles. Genotype × fertilisation interaction was significant in the environment with higher soil fertility. Sulfur addition improved N-recovery efficiency (0.15 v. 0.32) and agronomic efficiency of the available N (84 v. 93 g g–1) in the poor-fertility environment, characterised by their N and S deficiency and moderate level of organic matter. Grain N-recovery efficiency was largely explained by increases in grain number, whereas S recovery was also associated with increases in grain nutrient concentration. We conclude that genotype and environment strongly alter fertiliser-use efficiency, providing valuable information for ranking genotypes and optimising site-specific management of wheat crops in the Humid Pampa of Argentina. Grain S percentage may be useful as a physiological marker for selection of bread wheat genotypes with high apparent S recovery.

Hybrid sunflower seed yield, composition and deterioration after chemical desiccation

The impact of chemical desiccation on yield showed contrasting results depending on seedmoisture content at the time of application. Its effects on seed deterioration are still unknownand could be modified by seed composition. Objectives were to evaluate the impact of chemicaldesiccation on: i) hybrid sunflower seed yield and composition at harvest time, ii) seeddeterioration during long-term storage and iii) the relationship between seeds deterioration andoil or oleic acid content. Six hybrids including low, mid and high oleic were evaluated in threeexperiments. Two treatments were applied on female lines at 27-30% seed moisture:(i) spraying with Paraquat and (ii) detaching heads with a knife. Control remained in the fielduntil 10% seed moisture. Seeds were stored during 19 months under room and cold chamberconditions. Yield, number of seeds and hybrid seed composition (thousand seed weight, kernelpercentage, oil and acid oleic content) were determined. Seed deterioration during storage wasanalyzed by germination and vigour. Paraquat advanced harvest by 35-43 days, withoutaffecting yield or seed composition. During storage the germination of Paraquat treatmentsremained above that of control, without differences between storage conditions, while vigourremained above control only in cold chamber, for low oleic hybrids. Associations betweendeterioration (germination and vigour) and oil or oleic acid content, were not significant.Desiccation with Paraquat allows advanced harvest without yield losses or modifications in seedcomposition. The deterioration of desiccated seeds was lower and independent from oil andoleic acid content.